Gus Sinnis HAWC Review December 2007 Milagro a TeV Gamma-Ray Observatory Gus Sinnis Los Alamos...
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Gus SinnisHAWC Review December 2007
Milagro a TeV Gamma-Ray Observatory
Gus Sinnis
Los Alamos National Laboratory
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Gus SinnisHAWC Review December 2007
Milagro: A Summary of Results• 1991 Milagro proposal submitted to NSF & DOE
– Funding started in 1994 (ended in 1998 for central reservoir)
• 1997 (Milagrito) Evidence for TeV emission from a gamma-ray burst (3)
• 1997 (Milagrito) Detection of Mrk 501• 2000 Milagro begins physics operation• 2002 Detection of Crab Nebula• 2003 Detection of Mrk 421• 2004 Outriggers installed (funding from 2002-2004)• 2005 Discovery of Galactic diffuse emission• 2007 Discovery of TeV emission from Cygnus• 2007 Galactic Survey: 3 new sources 4 candidates• 2007 Cosmic-ray anisotropy: anomalous spectrum
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Gus SinnisHAWC Review December 2007
Complementarity of TeV Gamma-Ray Detectors
Imaging Air Cherenkov Telescopes Extensive Air Shower Arrays
Energy Range .05-50 TeVArea > 104 m2
Background Rejection > 99%Angular Resolution 0.05o
Energy Resolution ~15%Aperture 0.003 srDuty Cycle 10%
Energy Range 0.1-100 TeVArea > 104 m2
Background Rejection > 95%Angular Resolution 0.3o - 0.7o
Energy Resolution ~50%Aperture > 2 srDuty Cycle > 90%
High Resolution Energy SpectraPrecision Study of Known SourcesSource Location & MorphologyDeep Surveys of Limited Regions of Sky
Unbiased Complete Sky Survey Extended SourcesTransient Objects (GRB’s & AGN) Multi-Wavelength/Messenger Observations
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Gus SinnisHAWC Review December 2007
Current Generation EAS ArraysTibet AS
Milagro
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Gus SinnisHAWC Review December 2007
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Gus SinnisHAWC Review December 2007
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Gus SinnisHAWC Review December 2007
25 Northern Hemisphere Sources
Whipple 4 (1969 - 2006)HEGRA 4 (1992 - 2002)Milagro 4 (+3*) (2000 - present)HESS 6 (2004 - present)MAGIC 7 (2005 - present)VERITAS (coming soon!)
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Gus SinnisHAWC Review December 2007
Milagro
8 meters
e
80 meters
50 meters
• Water Cherenkov Detector• 2600m asl• 898 detectors
– 450(t)/273(b) in pond– 175 water tanks
• 4000 m2 / 4.0x104 m2 • 2-12 TeV median energy • 1700 Hz trigger rate• 0.5o-1.4o resolution• 95% background rejection
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Gus SinnisHAWC Review December 2007
Event Reconstruction
Measure time to <1 ns
Direction reconstruction 0.5o to 1.4o (size dependent)
Tim
e (n
s)
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Gus SinnisHAWC Review December 2007
Background Rejection in MilagroProton MC Proton MC
Data Data MC MC
Hadronic showers contain penetrating component: ’s & hadrons
– Cosmic-ray showers lead to clumpier bottom layer hit distributions– Gamma-ray showers give smooth hit distributions
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Gus SinnisHAWC Review December 2007
Background Rejection (Cont’d)
( )mxPE
nFitfOut+fTop=A
∗4
mxPE: maximum # PEs in bottom layer PMT
fTop: fraction of hit PMTs in Top layer
fOut: fraction of hit PMTs in Outriggers
nFit: # PMTs used in the angle reconstruction
Apply a cut on A4 to reject hadrons:A4 > 3 rejects 99% of Hadrons
retains 18% of Gammas
S/B increases with increasing A4
Background Rejection ParameterBackground Rejection Parameter
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Gus SinnisHAWC Review December 2007
Distribution of Excesses in the Galactic Plane
cut level
CrabNebula
Mrk 421
• 6.5 year data set (July 2000-January 2007)• Weighted analysis using A4 parameter• Crab nebula 15 • Galactic plane clearly visibleCygnus
Region
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Gus SinnisHAWC Review December 2007
• Milagro has discovered 3 new sources & 4 candidate sources in the Galaxy. • 5/7 of these TeV sources have GeV counterparts (only 13 GeV counterparts
in this region - excluding Crab) • Probability = 3x10-6
Abdo, et al. ApJ 2007
C3 J0634+17
Geminga
108 106
C4 J2226+60 EGRETE. Ona-Wilhelmi, et al., ICRC 2007
MGRO 1908+06
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Gus SinnisHAWC Review December 2007
H.E.S.S. A&A 2006
~-2.0 Ec ~20 TeV
The Highest Energy Gamma Rays: HESSRX J1713.7-3946 HESS Observations
3 years of data 2003-2005
4.8 above 30 TeV
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Gus SinnisHAWC Review December 2007
Milagro detection with median energy of 90 TeV.
Strong indicator of proton acceleration in this source.
1908+06 The Highest Energy Gamma Rays
Preliminary
Milagro data
6.4 x 10-11 E-2.05
20 TeV cutoff
7.6 @ 90 TeV
60 90
MGRO 1908+06
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Gus SinnisHAWC Review December 2007
The Cygnus Region
C1 J2044+36
C2 J2031+33
MGRO J2031+41MGRO J2019+37
• MGRO J2019+37: 10.9σ – Extended source 1.1o ± 0.5o (top hat dia.)– Possible Counterparts
• GeV J2020+3658, PWN G75.2+0.1• MGRO J2031+41: 6.9σ (5.0σ post-trials)
– Possible Counterparts:• 3EG J2033+4118, GEV J2035+4214• TEV J2032+413 (⅓ of Milagro flux)
– 3.0o ± 0.9o (top hat dia.)• C1 J2044+36: 5.5σ pre-trials
– no counterparts– < 2.0o
• C2 J2031+33: 5.3σ pre-trials– no counterparts– possible extension of MGRO J2019+37– possible fluctuation of MGRO J2019 tail &
diffuse emission & background• Tibet AS preliminary detections of 3
sources
5.8
4.5
3.8
Abdo, et al. ApJ 2007
Wang, et al. ICRC 2007
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Gus SinnisHAWC Review December 2007
TeV Galactic Diffuse Emission
Cygnus Region: Matter Density Contours overlaying Milagro Obs.
20 TeV profile in Cygnus Region w/GALPROP model
TeV excess possibly due to: a. Unresolved sources? b. CR accelerators?
pion componentIC component
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Gus SinnisHAWC Review December 2007
Mrk 421: 7 Year Multi-Wavelength Campaign
7 year data set July 2000 - May 2007No gamma/hadron cut (low energy)64 day averaging periodAverage flux is 67% of the Crab
Mila
gro
- E
vent
s/da
y
AS
M F
lux
cts/
s
MJD - 500001/1/2000 1/1/2001 1/1/2002 1/1/2003 1/1/2004 1/1/2005 1/1/2006 1/1/2007
May-July 2005
5 excess during x-ray quiescent period
Smith et al. ICRC 2007
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Gus SinnisHAWC Review December 2007
Significance
Fractional Excess x103
B A
AB
Walker, et al. ICRC 2007
Anisotropy of TeV Sky
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Gus SinnisHAWC Review December 2007
Anisotropy: What is it?
• Excess is not gamma rays
• Region A has a hard spectrum & a cutoff
• Points to a nearby cosmic-ray accelerator
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Gus SinnisHAWC Review December 2007
Future Synoptic TeV Telescopes
Complete summer 2007Chinese-Italian collaboration
4300m asl (YBJ, Tibet)RPC carpet
10-15 /√year on Crab
China-Japan collaboration4300m asl (YBJ, Tibet)
Tibet w/buried water tanksEmphasis 10-1000 TeV US-Mexico collaboration
4100m asl (Mexico)Water Cherenkov
>100 /√year on Crab
HAWC
ARGO
Tibet w/Muon Detectors
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Gus SinnisHAWC Review December 2007
• Milagro has made large advances in TeV survey technology– Discovery of diffuse TeV gamma rays from the Galactic plane & Cygnus– Discovery of at least 3 Galactic TeV sources (point and extended)– Highest energy gamma rays detected > 100 TeV– Anomalous cosmic-ray anisotropy observed– Demonstration of long-term AGN monitoring (enabling multi- observations)
• Others are beginning to propose similar detectors– Tibet w/muon– IHEP and Chinese Academy of Sciences proposing HAWC-like
detector (105 m2) for 2013 construction date
• Lessons Learned from Milagro– Optical isolation is important (angular resolution & energy resolution)– Altitude is critical for low-energy response– Larger area needed (bkgd rejection, angular res., & HE response)
• We are uniquely qualified to extend this technology to the next phase
Conclusions